It is technically difficult to include high levels (e.g., 10-20%) of liquid hydrophobic emollient oil (e.g., sunflower seed oil) and/or hydrophilic liquid humectant (e.g., glycerin) in a solid personal washing bar form and meanwhile maintain the bar mildness and benefit delivery to the human skin.
For example, high levels of humectants (e.g., glycerin, low MW polyalkylene glycol) can be trapped in a solid matrix of caboxylic fatty acid soap bar. However, it is known that carboxylic soap is harsh to skin especially when the soap concentration is high and when the soap is dissolved in the aqueous washing liquor through its own hydrophilic tendency or through the act of cosurfactants in the bar.
On the other hand, non-soap synthetic bar formulations are primarily structured by either hydrophobic crystalline materials such as free fatty acid or paraffin wax or by hydrophilic crystalline materials such as polyalkylene glycol of high molecular weight (e.g., MW between 2000 and 20000). While not wishing to be bound by theory, formulating high levels of emollient oil into a bar structured by the hydrophobic crystalline materials is believed to result in tightly binding the oil with the hydrophobic crystalline structurants. This contributes to the incapability of releasing the oil to water from the bar and may prevent delivering the oil to the skin via personal wash (see Example 1). Including liquid oils and/or liquid humectants in bars structured by hydrophilic crystalline materials leads to another difficulty. That is, the oil and the humectant are not compatible with the hydrophilic structurants, and this incompatibility results in oil leakage and phase separation from the bulk portion of the bar (see Example 1).
Therefore, a novel mild bar structuring system is required to be able to satisfactorily structure the oil and/or the humectant in the bar while simultaneously permitting oil release from the bar to the aqueous liquid and then to the human skin via the route of personal wash.
Novel to the art, the applicants of the subject invention found a specific group of polyol esters (i.e., having specific ranges of HLB and specific melting temperature) are capable of both structuring a high level of hydrophobic emollient oils and/or humectants in solid personal washing bars while still permitting the oil and humectants to be released from the bar into aqueous liquor to be delivered to the human skin through the route of personal wash. Using the polyol esters with specific hydrophilic-lipophilic balance (HLB), balancing the ratio between polyol ester and oil/humectant, and balancing the ratio between polyol ester to other structurants are critical to achieve the desired oil structuring and oil releasing.
The use of polyol esters in personal washing bars is not new.
European Patent Application EP 94105052.8 assigned to Kao Corp. (invented by M. Tonomura and T. Ohtomo), for example, teaches the use of monoglycerides to boost the lather of formulations comprising only nonionic surfactants. The application does not teach the use of the combination of specific solid monoglycerides and high level of liquid emollient oils/humectants to make bars, preferably pourable, cast melt bars, preferably comprising anionic surfactants and amphoteric surfactants. By contrast, the subject invention found that by using a specific polyol ester (e.g., specific range of HLB, polyol ester to oil/humectant ratio, and polyol ester to other structurant ratio), high levels of emollient oil and/or humectants can be satisfactorily incorporated into bars for skin benefit.
An international application published under PCT WO 92/13060 to Procter & Gamble (authored by R. James) teaches the use of monoglycerides in general, PEG and fatty acid as binders for an extruded syndet bar formulation. The prior art, however, does not teach the use of a specific combination of specific monoglycerides (e.g., specific ranges of HLB) and PEG and fatty acid to incorporate high level of liquid emollients (e.g., vegetable oils)/liquid humectants (e.g., glycerin) to make a bar, preferably pourable, cast melt bar. The prior art also does not teach the specific bar formulation spaces to ensure that high levels of liquid oils and/or humectants can be structured in the solid bar matrixes and can be delivered to skin via personal wash. In contrast, the subject invention found that by using a specific polyol ester (e.g., polyol esters with specific range of HLB, specific polyol ester to oil ratio, and specific polyol ester to other structurant (e.g., PEG and fatty acid) ratio), high levels of emollient oil and/or humectants can be satisfactorily incorporated into bars and can be delivered from the bars to skin under the personal wash condition.
U.S. Pat. No. 5,510,050 to J. Dunbar, P. Beerse, and E. Walker also teaches the use of monoglycerides in general as a non-preferred candidate for the plasticizers in an extruded cleansing bar containing liquid polyols (4-15%) and magnesium soap (4.5 to 50%). The preferred plasticizers are fatty acids, sodium soap, and paraffin wax (Column 5, line 22-24). The prior art, however, does not teach the use of a specific combination of specific monoglycerides (e.g., specific ranges of HLB) and other plasticizers to incorporate high level of liquid emollients (e.g., vegetable oils)/liquid humectants (e.g., glycerin) into a bar, preferably pourable, cast melt bar. The prior art also does not teach the specific bar formulation spaces to ensure that high levels of liquid oils and/or humectants can be structured in the solid bar matrixes and can be delivered to skin via personal wash. In fact, as found by the subject invention, the preferred plasticizers used in the prior art hinder the skin deposition of liquid oils from bars to skin. The prior art has to use magnesium soap as the key ingredient to aid processing (column 2, line 26). In contrast, the subject invention found that by using a specific polyol ester (e.g., polyol esters with specific range of HLB, specific polyol ester to oil ratio, and specific polyol ester to other structurant (e.g., PEG and fatty acid) ratio), high levels of emollient oil and/or liquid humectants can be satisfactorily incorporated into bars and can be delivered from the bars to skin under the personal wash condition. In the subject invention, carboxylic acid soap in general is an optional ingredient. Said soap causes skin irritation and is preferred to be used at about below 4% wt. of total bar composition in the subject application.
A Great Britain Patent GB 1,570,142 assigned to GAF Corp. teaches the use of both hardened triglycerides and fatty alcohols as the plasticizers in an extruded syndet formulation. In contrast to the subject invention, the prior art does not teach the use of the combination of specific monoglycerides and high level of liquid emollient/humectants to make bars. By contrast, the subject invention found that by using a specific polyol ester (e.g., specific range of HLB, polyol ester to oil ratio, and polyol ester to other structurant ratio), high levels of emollient oil and liquid humectants can be satisfactorily incorporated in the bar and can be delivered to skin via skin cleansing for the purpose of skin moisturization.
In summary, none of the references, alone or in combination teach that the use of specific polyol esters (e.g., having specific melting temperature, especially specific hydrophobic-lipophobic balance (HLB)) in specific bar compositions (i.e., containing greater than or equal to 5% hydrophobic emollient oils and/or humectants, the polyol ester to oil/humectant ratio greater or equal to 1:1, and the polyol ester to other structurant ratio greater than 1:1) will result in bars, preferably pourable cast melt bars, with enhanced oil/humectant carrying and releasing capabilities. These capabilities are crucial to benefit delivery to the skin via personal wash.